Adaptive Multi‐degree of Freedom Self‐Oscillation in Fluids for Active Biodetection

Abstract A self‐oscillator is a flexible device capable of autonomously generating periodic oscillatory motion in response to a constant external stimulus. Limited by high damping forces in fluids, realizing self‐oscillatory with multiple degrees of freedom and high frequencies in fluids remains a great challenge. Here, a homogeneous Polypyrrole (PPy) and MXene permeable dual‐network poly( N ‐isopropyl acrylamide)/PPy/MXene hydrogel (PPM) self‐sustained oscillator (PPMBOT) is designed by a one‐pot synthesis and low‐temperature in situ polymerization strategy, which exhibits multiple degrees of freedom and high‐frequency oscillation. Its oscillation frequency is ≈2.05 Hz, almost the highest among the reported multidirectional oscillators operating in fluids. This self‐oscillatory mechanism is due to the self‐shadowing effect in the dynamic light–material interaction and results from a built‐in negative feedback loop based on it, which is facilitated by the efficient contraction and expansion of the PPM. A novel actively trappable biosensor is proposed based on the PPMBOT, which increases the binding efficiency of the electrode to the target biomolecules through the self‐oscillatory motion and efficient solution replacement within the micropore of the PPM, realizing an ultrasensitive detection limit of 0.39 fg mL −1 . The concept of an actively capturable biosensor provides broader ideas for both the application of self‐oscillation and biomedical detection.